In a mobile communication device, such as a portable telephone (hereinafter referred to as `mobile station`), a power source is supplied from a battery, and battery consumption at the mobile station is an important factor which determines the performance of the mobile station. Therefore, it is generally conducted that a consumed current of circuit is designed as low as possible and a power source is supplied only by real operation time to each circuit block.
However, when the mobile station has a reception function, the mobile station always needs to monitor a control signal from a base station to the mobile station to receive a call signal. Also in this case, to save the battery consumption as much as possible, the control signal from the base station is intermittently received for a predetermined period which is determined between the base station and the mobile station. This period is generally called `battery saving period`.
Taking the case of a second-generation cordless telephone such as PHS, just after turning on the power switch of the mobile station or when no control signal from the base station can be caught, e.g., since the mobile station is out of any service area, some functions of the mobile station including a receiving circuit are turned on to start an operation of catching the control signal from the base station (hereinafter referred to as `base station search`).
After catching the control signal once, the mobile station conducts an operation, i.e., waiting operation, that intermittently turns on the power source to some functions to receive the control signal to the mobile station for a battery saving period allowed by the system. In the waiting operation, no power source is supplied to any functions other than a timer circuit for measuring the battery saving period expect when the control signal is received.
When the mobile station is out of any service area, the battery saving operation is conducted to save the battery consumption since the base search station must be continued when the power source of the mobile station is switched on.
Meanwhile, in the second-generation cordless telephone system, the service area of a base station is set to have a diameter of about 100 to 200 meters and a service for the mobile station's high-speed movement is not considered. During the high-speed movement of the mobile station, where is moves out of a service area or to the nearby service area for about five minutes, the regular service cannot be obtained. However, if the power source continues to be switched on in such a case, the receiving circuit on operation frequently conducts the catching of a control signal to waste the battery despite no regular service when entering a new service area. Therefore, the mobile station telephone conducts the battery saving operation while judging the high-speed movement.
For example, a conventional portable telephone with such functions is disclosed in Japanese patent application laid-open No. 7-87010 (1995). FIG. 1 shows a circuit composition of this portable telephone with the battery saving function, and FIG. 2 is a flow chart for explaining the operation.
Some functions of the portable telephone are driven by a battery 86. The battery 86 always drives a timer 84 and a control signal reception counter 83. The other circuits, such as a receiving circuit 81 and a controller 82 are driven by a power circuit 85 powered by the battery 86. The power supplying operation of the power circuit 85 is controlled by a power source control signal from the timer 84.
The receiving circuit 81, which operates when a power source voltage thereto is supplied from the power circuit 85, demodulates a signal received from a radio circuit into reception data and sends it to the controller 82.
The controller 82 conducts a base station search operation to catch a control signal from the receiving circuit 81 just after the power source switch is turned on, and it sends instructions to the timer 84 and conducts the battery saving operation after the base station is caught. In the battery saving operation, it starts operating by receiving an interrupt signal from the timer 84, and it judges whether the mobile station is out of a service area of the base station or moving at a high speed by monitoring the control signal from the receiving circuit 81 and then sends instructions to the timer 84. When the mobile station moves out of the current service area, it is judged from a value of the control signal reception counter 83 whether it is moving at a high-speed.
When the controller 82 judges that the mobile station is within the service area from a caught control signal, it sends instructions to the timer 84 to conduct a battery saving operation for receiving a designated control signal, which is explained again later. The timer 84 actuates its internal timer TMs for the battery saving operation for reeving the designated control signal.
The timer 84 comprises the timer TMs for determining a battery saving period after catching a control signal from the base station in the base station search and a timer TM1 for determining a battery saving period in the case of catching no control signal from the base station. In the battery saving operation, these timers TMs, TM1 are actuated by the controller 82 to measure respective predetermined times to stop the operation of the power circuit 85. During this time measurements, the timer 84 gives the power source control signal to the power circuit 85 and further gives an interrupt according to the timer TMS or TM1 to the controller 82.
The control signal reception counter 83 receives a specific signal in a control signal received by the receiving circuit 81 and counts the reception number of the specific signal. From the reception number, it is judged whether the mobile station is moving at a high speed.
Next, the battery saving operation will be explained in FIG. 2.
By a control signal transmitted from the base station, a frame including a broadcast control channel(BCCH), several paging channels(PCHs) and a signaling control channel(SCCH) is repeatedly transmitted. The broadcast control channel (BCCH) serves as a frame synchronizing signal. One of the paging channels (PCHs) is corresponding to the mobile station itself.
When the mobile station is within the service area of a base station, the battery saving operation starts after a control signal is caught in the base station search and the position registration is completed. The battery saving operation is conducted with a frame unit between paging channels (PCHs) corresponding the mobile station itself. The period of the battery saving operation is determined by the timer TMs of the timer 84. In one battery saving period, the power source is supplied to the receiving circuit 81 etc. by the power circuit 85 only for the period of a paging channel (PCH) corresponding to the mobile station itself.
When the mobile station is out of the service area of a base station or moving at a high speed, a base station search to intermittently catch a control signal is conducted and a battery saving operation for this search is conducted. In this case, the timer 84 determines a battery saving period by the timer TM1. In this battery saving period, the power circuit 85 is controlled to be turned off except a period for catching the control signal. The battery saving period when the mobile station is out of the service area or moving at a high speed is set to be much longer than that in the base station search when it is within the service area, thereby reducing the consumption of the battery 86.
During the battery saving operation, the timers TMs, TM1 measures the power source stopping period, and the power circuit 85 is controlled to stop the power source supplying operation during the measurement. After completing the measurement of the power source stopping period, the timer 84 instructs the power circuit 85 to start the power source supplying operation, and then the power source is supplied to functional circuits, such as the receiving circuit 81 and controller 82. Together with the supplying of power source, the timer 84 gives an interrupt according to the timer TMs or TM1 to the controller 82.
When this interrupt is received, the controller 82 starts the flow process of searching a control signal as shown in FIG. 2. At Step S701, it is judged that the interrupt is sent from which of the timers TMs, TM1. If the interrupt is sent from the timer TM1, which means to be on base station search, catching of a control signal is conducted at Step S711. In this case, the power source turn-on time is set to be sufficiently longer than the period of a paging channel (PCH) in order to surely catch the control signal in the base station search when entering the service area.
When a paging channel (PCH) is caught at Step S711 or the power source turn-on time is passed without catching the paging channel (PCH), it proceeds to the following Step S712. At Step S712, it is judged whether the paging channel (PCH) signal is caught. If the paging channel (PCH) signal is not caught, the timer TM1 is actuated to measure the battery saving period to stop the power source at Step S707. When the timer TM1 is actuated, the timer 84 sends the power source control signal to turn off the power circuit 85 and the controller 82 waits for the next timer interrupt. Thus, the waiting operation continues.
Moving from the outside to inside of a service area is judged by that the paging channel (PCH) signal is caught at Step S712. In this case, after adding one to the control signal reception counter 83 at Step S713, the timer TMs is actuated setting a power source stopping period at Step S714. When the timer TMs is actuated, the timer 84 sends instructions through the power source control signal to turn off the power circuit 85. The controller 82 waits for the next timer interrupt. Thus, when the paging channel (PCH) signal is caught, it proceeds to the control signal waiting operation for the case that the mobile station is within a service area.
Next, a case that a process is started by an interrupt generated when the measurement of the timer TMs is completed during the control signal waiting operation will be explained below.
When it is judged by the controller 82 at Step S701 that the interrupt is sent from the timer TMs, which means that the mobile station is waiting for a control signal within a service area, it proceeds to Step S702. When the paging channel (PCH) signal is received within a wait time corresponding to the paging channel (PCH) period or the wait time is passed without receiving the paging channel (PCH) signal, it proceeds to Step S703. At Step S703, it is judged whether the paging channel (PCH) signal is received. If the paging channel (PCH) signal is received, it proceeds to Step S713 after clearing a reception failure number counter. At Step S713, the control signal reception counter 83 for counting how many times the paging channel (PCH) signals are received in the current service area is added by one. The count value of the control signal reception counter 83 is used to judge as to whether it is moving at a high speed, as explained later.
At Step S714, the timer TMs is actuated setting a power source stopping period, which is obtained by subtracting the time required to receive a PCH signal and the reception preparing time from a battery saving period for within a service area. When the timer TMs is actuated, the power circuit 85 is turned off by the power source control signal from the timer 84. Then, the controller 82 waits for the next timer interrupt. Thus, the waiting operation with the battery saving period for within a service area continues.
If the paging channel (PCH) signal is not received at Step S702, the reception failure number counter is added by one at Step S704 and then it is judged whether the value of the reception failure number counter, i.e., the number of continuous reception failures, is a reference value M, e.g., M=b 2, or more.
If the continuous failure number is less than the reference value M, it proceeds to Step S715 and the timer TMs is actuated setting a power source stopping period, which is obtained by subtracting the paging channel (PCH) time from a battery saving period for within a service area. When the timer TMs is actuated, the power circuit 85 is turned off by the power source control signal from the timer 84. Then, the controller 82 waits for the next timer interrupt. Thus, when the next interrupt is generated, the waiting operation with a period corresponding to the battery saving operation is conducted again at Step S702.
If the continuous failure number is the reference value M or more at Step S704, the reception failure number counter is cleared, and then it proceeds to Step S705. This is a case that moves outside the service area where it stayed until then. At Step S705, it is judged whether it is moving at a high speed. It is estimated that, during the high-speed movement, the number of receiving the paging channel (PCH) signal within the service area where it stayed until then is smaller than that in the case of other than during the high-speed movement since the service area changes in several seconds. Therefore, by setting a suitable reference value M and comparing it with the value of the control signal reception counter 83, it can be judged whether it is moving at a high speed.
If the value of the control signal reception counter 83 is less than the reference value M at Step S705, it is judged that it is moving at a high speed, and then it proceeds to Step S706. After clearing the control signal reception counter 83 at Step S706, the timer TM1 is actuated setting the power source stopping time with the battery saving period for outside of a service area at Step S707. When the timer TM1 is actuated, the power circuit 85 is turned off by the power source control signal from the timer 84. Then, the controller 82 waits for the next timer interrupt. Thus, during the high-speed movement, the intermittent base station search operation is conducted.
If the value of the control signal reception counter 83 is the reference value M or more at Step S705, it is judged that it moves outside the service area where it stayed until then not moving at a high speed, and then it proceeds to Step S711 after clearing the control signal reception counter 83 at Step S708. As described earlier, at Step S711, the paging channel (PCH) catching operation with the battery saving period for outside of a service area is conducted.
If the paging channel (PCH) signal is caught at Step S711, which means that the mobile station moves to the nearby service area, it proceeds through Step S712 to Step S713 where the control signal reception counter 83 is added by one, thereafter it proceeds to Step S714. At Step S714, the timer TMs is actuated setting a power source stopping period, which is obtained by subtracting the time required to receive a PCH signal and the reception preparing time from a battery saving period for within a service area. Thus, the waiting operation with a period corresponding to the battery saving operation is conducted, within the service area.
If the paging channel (PCH) signal is not caught at Step S711, which means that the mobile station moves outside of all the service area, it proceeds through Step S712 to Step S706 where the control signal reception counter 83 is cleared, thereafter it proceeds to Step S707. At Step S707, the timer TM1 is actuated setting a power source stopping period with the battery saving period for out of the service area. Thereby, the intermittent base station search operation for out of the service area is conducted.
As described above, when the mobile station is out of the service area of a base station or moving at a high speed, the intermittent base station search operation with a battery saving period which is much longer than that in case of within a service area of the base station is conducted. Therefore, the battery consumption during the high-speed movement can be saved.
In the conventional mobile communication device, whether the mobile station is moving at a high speed or not is judged from the PCH signal reception number in the waiting operation of a paging channel (PCH) signal. However, in this method, it may be judged that the mobile station is moving at a high speed even when the PCH signal cannot be temporarily received due to, e.g., an external noise. In such a case, the power source stopping period continues for a long time. When a local call is proceeded at that time, a loss at called station must be occurred. It damages the performance of the mobile communication device.
Furthermore, when the mobile station is moving at a high speed or out of any service area, the base station search operation with a period longer than the battery saving period for within a service area and a long power stopping period is intermittently conducted. However, this intermittent operation, which is only of two stages, cannot give a sufficient battery saving operation and reduce substantially the battery consumption. Namely, it is a problem that, regardless of the different situations that it is moving at a high speed and that it is out of any service area, only one power source stopping period is set.